Experiment Retrospection

    Tool-Chip Thermocouple Technique

    Here is the schematic of tool-chip thermocouple set-up:

    Generally, only the average temperature at the tool/chip interface can be obtained. Sometimes, a tool-work thermocouple was also used.

     The calibration of the tool-chip thermocouple is shown as:

    Some limitations of this methods are mainly:
     
     

    1. The elimination of parasitic e.m.f.'s which could affect the thermocouple output.
    2. The calibration of the thermocouple output.

    2. Embedded Thermocouple Technique

    The following is a typical embedded thermocouple setup:

     
     

    3. Infrared Radiation Technique

    The first use of this technique was reported by Schwerd who developed a total Radiation Pyrometer for determining the temperature distribution at the surfaces of tool and workpiece.

     Several researchers attempted to access to chip/tool interface by scanning through holes drilled either in the work or tool. Prins' pyrometer arrangement is shown as follows:

     Limitation of the above measurements is that there is considerable interference of the contact zone which must influence the heat flow and the resulting temperature of either the chip or tool surface.

    Infrared Photography technique proposed by Boothroyd can obtain a full temperature field in the chip and workpiece. A calibration strip, which was electrocally heated from one end,was simply used to calculate the real temperature. The following setup was used at that time:

    Today, many disavantages of this technique are overcomed.
     
     

    4. Metal Microstructure and Microhardness Variation Measurement

    Under suitable cutting conditions, the metallographic method can be used to determining the temperature gradients in high speed steel cutting tools. The following picture is the etched rake face of tool used to cut nickel in normal dry atmosphere at 46 m/min, 0.25 mm/rev feed for 30 seconds(After E. F. Smart and E. M. Trent):

    However, the microstructure, microhardness and other properties change to some extent dependent on temperature and time.
     
     

    5. Thermosensitive Painting Technique

    Using the thermosensitive paints for estimating cutting temperature is because that these paints change colors at different temperature.

     Limitations are that there is a relatively long time lag for the colors to change and that small changes in temperature are not easy to be detected.
     
     

    6. Temper Color Technique

    This technique is based on the fact that the temper colors of some metals are different at different temperatures. And it wasn't widely used.